Homogeneous networks are networks which are typically deployed using a macro-centric planned process. A homogeneous network is a network of base stations in a planned layout, in which all base stations have similar transmit powers, antenna patterns and similar backhaul connectivity to a core network. The locations of base stations are typically chosen during the network planning phase and base station settings are configured to maximize coverage and control interference between multiple base stations. As traffic demand grows and the radio environment changes, the network relies on cell splitting or additional carriers to increase capacity and overcome link budget limitations to maintain a uniform user experience.
Heterogeneous networks involve utilizing a diverse set of base stations deployed to improve capacity. A heterogeneous network may contain a macro base station, several overlaid pico stations, femto base stations, remote radio heads, relay base stations or a combination of these components. A base station can be understood as a node B, an evolved node B (eNB), a network node, or an access node. The overlaid base stations may operate on the same radio frequency or on different radio frequencies. The macro base station typically transmits at a high power level while the other base stations transmit at relatively lower power levels. The connections between the base stations may be through fibre or cable. In some examples, such as femto base stations, the base stations may be connected to the core network through the Internet. Macro base stations and relay base stations are connected to each other through a wireless backhaul link in some embodiments. In this case, the macro base station is called the donor base station and has gateway functionality. Such a base station may also be referred to herein as an access node.
The use of multiple base stations with different power levels in the same cell may lead to interference between the base stations. For example, as the macro base station typically transmits at a high power level while other base stations transmit at relatively lower power levels, a user equipment (UE) that may see higher signal to interference noise ratio (SINR) or received signal power from the macro base station may actually have a lower path loss to a lower power base station. Based on the received signal powers, the UE may select the macro base station as its target base station. During a random access to the macro base station, the UE following a random access channel procedure (RACH) may use a physical random access channel (PRACH) with a high power that may cause random access interference to the lower power base station on uplink resources for other UEs serviced by the lower power base station.